1. Field of the Invention
This invention relates to potato chips. More particularly, it relates to potato chips having a low fat content. This invention especially relates to low fat content potato chips prepared by microwave heating.
2. Description of the Prior Art
In the conventional production of potato chips, raw or blanched potato slices are deep fat fried to yield the final edible potato chip. The effect of frying on the potato slices is to reduce the water content (fresh potatoes contain approximately 85% moisture) with consequent oil uptake and to produce surface color and crispness. The finished potato chips contain from 30-45% oil or fat based on the total weight of the potato chip and less than 5% moisture. (As used herein all percentages are expressed in weight unless stated to the contrary and the term "fat" is to be understood to include both edible fats and oils.) This high fat content is undesirable for many reasons. For example, it increases the total caloric content of the potato chip making such a product objectionable to persons wishing to lose weight or to avoid weight gain. The deep fat frying process also shortens the shelf stability of the potato chip. Moreover, the frying process is difficult to control and often results in excessively cooked potato chips. A low fat content chip cannot be made with deep fat frying processes and the fat content cannot be controlled as fat is absorbed throughout the frying operation.
Potato chips having a fat content below 30-45% have been prepared heretofore. U.S. Pat. No. 3,402,049 of Mancuso et al. discloses a method of producing potato chips having an edible oil or fat content of from about 20 to about 30%. Deep fat frying is not employed by Mancuso et al. to obtain this lower fat content. The raw potato slices are soaked in an edible fat at a temperature below the gelatinization temperature of potato starch, removed from the fat, drained and heated in an oven or by forced air drying at temperatures of 225.degree.-350.degree. F. until the desired degree of browning is achieved.
Oil uptake is also reduced in a process disclosed in British Pat. No. 1,034,035 where reductions in oil content of 10-20% are obtained. Here, the potato slices are removed from the deep fat fryer when their water content is still relatively high (5-20%) and then dried by a heating process without further oil uptake. The heating completes the required water extraction and the necessary degree of browning and may be achieved by a combination of hot air drying followed by microwave heating. The first drying stage is relatively slow and the second is relatively fast. Oil uptake is reported as 10-20% less than in the conventional frying process. Others have reported that microwave drying of partially deep fried potato chips resulted in oil contents of about 32-38% compared to 38-44% for those which were finished fried in the conventional manner (Davis & Smith, "Microwave Processing of Potato Chips" 72,86-88, Potato Chipper (November, 1965).
Heating or drying of potato chips has been achieved heretofore by a variety of procedures. Hot air drying is disclosed in U.S. Pat. No. 3,402,049 and British Pat. No. 1,034,035 (discussed above) as well as in U.S. Pat. No. 3,044,880 of Bogyo et al., while radiant heat drying to remove water from potato chips is disclosed in U.S. Pat. No. 3,353,962 of Smith, Jr.
Microwave heating is a relatively new procedure employed in the production of potato chips. British Pat. No. 1,034,035 discloses microwave drying for the removal of some of the water from partially deep fried potato chips. U.S. Pat. No. 3,365,301 of Lipoma et al. discloses the use of microwave heating to supplement the cooking of potato slices. Here, raw potato slices are deep fried to the desired oil content but short of any substantial color change and then the desired moisture content and degree of crispness is obtained by exposure of the partially cooked chips to microwave energy. This procedure of partially frying the potato slices and completing the process in a microwave oven, as well as the commercial use of this procedure, is discussed in Talburt and Smith, "Potato Processing," 287-290 (The Avi Publishing Company, Inc. 1967).
The combination of a deep fat fryer and a microwave oven for the cooking of foodstuffs is disclosed in U.S. Pat. No. 2,997,566 to Pierce et al. The deep fryer is provided with an external source of heating to heat and maintain the cooking fat at temperature. The microwave energy cooks the foodstuff while the cooking fat browns the exterior of the foodstuff to provide the desired surface finishing and sealing. It has been suggested that this combination apparatus may provide very low fat absorption (Copson, "Microwave Heating," 375 (The Avi Publishing Company, Inc. 1962)). Copson also suggests the substitution of a non-toxic, flavorless resin, such as a silicone, for the cooking fat or oil in the combination deep fat fryer-microwave oven to provide "fat-free" deep fat frying. However, the elimination of the reservoir of liquid cooking medium within the microwave oven has not been suggested by either Pierce et al. or Copson.
Microwave heating is employed as one of the steps in a process of producing dehydrated french fried potatoes disclosed in U.S. Pat. No. 3,881,028 to Capossela, Jr. et al. Prior to deep fat frying, the potatoes are subjected to microwave heating which causes a minimal water loss of 2.5-3.0% but, more importantly, causes a degree of gelatinization throughout the potato piece which is critical in producing the dehydrated french fried product. However, although dehydration is effected in the deep frying and a final heating stage, reducing the water content more than 3% by microwave heating prior to deep fat frying is said to produce an unduly hard and dry french fry because of excessive starch gelatinization.
Heretofore, neither low fat potato chips nor conventional potato chips have been produced by a process which eliminates completely immersion frying of the potato pieces and utilizes a single step of heating by microwaves to remove water and produce a crispy product having the uniform color and taste of deep fried potato chips.
It is an object of this invention to provide potato chips by a process which eliminates deep fat frying.
It is another object of this invention to provide potato chips having a fat content significantly lower than that obtained heretofore by commercial processes.
It is still another object of this invention to provide potato chips by a process which utilizes microwave heating as the sole means of reducing the water content of the potato piece to the required level and providing the color, crispness and flavor of deep fried potato chips.